Noises emitting from the AES power plant in Redondo Beach are the result of steam being released from safety valves inside the plant, said Eric Pendegraft, president of AES Southland, the company that owns the facility on Harbor Drive.

Residents near the plant reported loud noises in July and again on Wednesday around 11:30 p.m.

Steam-release valves are built-in safety devices used to prevent problems that can occur in normal operating conditions, Pendegraft said. Specifically, the equipment is used to prevent rupturing tanks or piping.

When an energy production unit is started up to produce electricity, pressure can build up inside the piping. Safety valves are in place to release any of that excess pressure. Water vapor and steam will rise from smokestacks when an incident does occur.

“It’s a lot of complicated and sophisticated equipment and sometimes it doesn’t operate as it’s designed,” Pendegraft said. “That’s what the safety devices are there for.”

Chavez said the steam release didn’t pose any health or safety threats.

“It’s not a normal circumstance, and we don’t like it to happen,” Chavez said. “But there are no safety issues; the sounds just mean the equipment is doing its job. It happens at every power plant.”

The systems are monitored jointly by workers and computer systems.

Shortly after the noises occurred Wednesday, Facebook and Twitter users were busy inquiring to see if anyone else had heard the strange sounds.

South Bay resident David Kartsonis described the noise as a combination of rolling thunder and an engine backfiring. It lasted for about 15 to 30 seconds, he said.

“It was pretty loud. I can’t imagine anyone not hearing it unless their TV was way up,” he said.

Hermosa Beach resident Joe Capallero remembered hearing the sounds emitting from the power plant in July as he walked down Herondo Street one afternoon.

“I saw people running out of their apartment buildings and condos, looking up to the sky like we were being invaded,” he said.

Pendegraft said the company will typically receive a few complaints after the noises occur, and they can come again anytime.

“There may be ways to muffle it but we haven’t done any studies,” Pendegraft said. “I cannot say with absolute certainty that it won’t happen in the future.”